Risk is one of those things that one person cannot really define for another, since each person thinks about risks in their own personal way.
In other words it is not possible for us to say whether the pipelines in Contra Costa County are safe enough. All we can do is to try to provide enough information so individuals can make that decision on their own, and then work with others in their community to set policies based on the beliefs of as many people as possible.
Risk is made up of two different factors both of which need to be carefully considered when deciding how risky an activity is. Those factors are the probability that an event will occur (chance a pipeline will rupture or leak), and the possible consequences if it does.
PHMSA maintains a publicly accessible database of reported pipeline incidents. The map below shows the Significant Incidents in California from 2010 to present. If you click on the incident dot some basic information about the incident will open up.